1. Field of the Invention
The present invention relates to a positive resist composition suitable for use in the ultramicrolithography process such as production of VLSI or a high-capacity microchip or in other photofabrication processes. More specifically, the present invention relates to a positive photoresist capable of forming a high-resolution pattern by using electron beam, X-ray or EUV, that is, a positive resist composition suitably usable for fine processing of a semiconductor device, and a pattern forming method using the same.
2. Description of the Related Art
In the process of producing a semiconductor device such as IC and LSI, fine processing by lithography using a photoresist composition has been conventionally performed. Recently, the integration degree of an integrated circuit is becoming higher and formation of an ultrafine pattern in the sub-micron or quarter-micron region is required. To cope with this requirement, the exposure wavelength also tends to become shorter, for example, from g line to i line or further to KrF excimer laser light. At present, other than the excimer laser light, development of lithography using electron beam, X ray or EUV light is proceeding.
The lithography using electron beam or EUV light is positioned as a next-generation or next-next-generation pattern formation technique and a high-sensitivity high-resolution resist is being demanded. Particularly, in order to shorten the wafer processing time, the elevation of sensitivity is very important, but when high sensitivity of a positive resist to electron beam or EUV is sought for, not only reduction in the resolution but also worsening of the iso/dense bias are incurred and development of a resist satisfying these properties at the same time is strongly demanded. The iso/dense bias as used herein means a difference in the pattern dimension between a high density portion and a low density portion of a resist pattern and when this difference is large, the process margin is disadvantageously narrowed at the actual pattern formation. How to reduce this difference is one of important problems to be solved in the resist technology development. The high sensitivity is in a trade-off relationship with high resolution, good pattern profile and good iso/dense bias and it is very important how to satisfy these properties at the same time.
In the actual field of semiconductor fine processing, the aging stability of the resist composition is a problem. Usually, in producing VLSI or a high-capacity microchip, there is employed a system of preparing and storing only a resist composition in a large amount and step-by-step using a necessary amount of the resist therefrom at the semiconductor fine processing. However, the conventional resist composition for electron beam or EUV undergoes a change in sensitivity with aging and this requires to vary the exposure amount, development conditions and the like between when using a resist immediately after preparation and when using a resist at a later time after the preparation, which hampers mass production.
With respect to such a positive resist, there are conventionally known some resist compositions using a phenolic acid-decomposable resin obtained by copolymerizing an acid-decomposable acrylate monomer having an alicyclic group as the acid-decomposable group. Examples thereof include positive resist compositions disclosed in U.S. Pat. No. 5,561,194, JP-A-2001-166474 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-2001-166478, -A-2003-107708, JP-A-2001-194792 and JP-A-2005-234434. Also, a case using a compound capable of generating a sulfonic acid upon irradiation with an actinic ray or radiation and a compound capable of generating a carboxylic acid is disclosed in JP-A-2003-107707.
In these resist compositions using a low-molecular phenol compound as the main component, high dissolution contrast may be obtained but, on the other hand, there is a problem that the performances in terms of iso/dense bias and exposure margin are insufficient.